A tire with a radial carcass reinforcement usually comprises a reinforcing bead core in each bead portion of the tire, about which the carcass reinforcement is anchored by winding or forming an upturn. The bead cores provide a claming force for the tire when the tire is mounted upon the beads seats of a wheel rim. The clamping produces a certain compression of the bead portion between the bead core and the wheel rim, the clamping generally being brought about by a difference in the angles of the bead set and the rim seat respectively, and/or by a difference in the diameters of said seats.
The bead clamping force of the tire is particularly important in designing a run-flat tire or tire system. One such tire system that uses the clamping force to maintain operation of the tire during underinflated or uninflated operating conditions is disclosed in U.S. Pat. Nos. 5,785,781 and 5,971,047. The radial carcass reinforcement of the tire, which is anchored within each bead to at least one inextensible annular reinforcement element, has a profile, when the tire is mounted on its operating rim and inflated to its operating pressure, with a direction of curvature which is constant in the sidewalls and bead regions which ends in the bead toe. The preferred bead region of this type of tire is more fully disclosed in U.S. Pat. No. 5,971,047, wherein the carcass reinforcement has a hooking structure.
In the tire of the above disclosed run-flat system, when the tire system is inflated at reduced or zero pressure, the beads of the tire remain in place when travelling as the structure creates an increase of the clamping of the bead toe on the mounting rim as a function of the tension of the carcass reinforcement. The structure also makes it possible to have initial clamping on rim of low value, given that said clamping will increase when the tire is inflated to its recommended pressure.
However, due to the turn back of the carcass reinforcement ply below the bead core, the above tire structure is complicated and difficult to implement industrially, and is therefore expensive.